Insulating layer-forming compositions, also referred to as intumescent compositions, are usually applied on the surface of components, in order to form coatings for the purpose of protecting these components from fire or from the effect of a high degree of heat as a result of a fire. In the meantime steel structures have become an integral part of modern architecture, even if they have a distinct disadvantage compared to reinforced concrete construction. At temperatures exceeding approximately 500 deg. C., the load bearing capacity of steel drops by 50%. That is, the steel loses its stability and load bearing capacity. This temperature can be reached, as a function of the fire load, for example, during direct exposure to fire (approximately 1,000 deg. C.), after about 5 to 10 minutes, a situation that often leads to a loss in the load bearing capacity of the structure. At the present time the goal of fire retardation, in particular, the fire retardation of steel, is to delay as long as possible the time it takes for a steel structure to lose its load bearing capacity in the event of a fire for the purpose of saving human lives and valuable assets.
For this purpose the building regulations in many countries require commensurate periods of fire resistance for certain structures made of steel. These periods are defined by means of the so-called
F classes, such as F 30, F 60, F 90 (fire resistance classes in compliance with DIN 4102-2) or the American classes in compliance with ASTM etc. In this respect F 30 according to DIN 4102-2 means, for example, that in the event of a fire the load bearing steel structure has to withstand the fire for at least 30 minutes under standard conditions. This requirement is usually met by delaying the rate of the temperature rise of the steel, for example, by coating the steel structure with intumescent coatings. In this case it involves paints with constituents that foam to form a solid microporous carbon foam in the event of a fire. At the same time a fine pored and thick foam layer, the so-called ash crust is formed. This foam layer has high heat insulating properties, as a function of the composition, and, as a result, delays the temperature rise of the component, so that the critical temperature of approximately 500 deg. C. is reached no later than after 30, 60, 90, 120 minutes or up to 240 minutes. The crucial feature for the achievable fire resistance is the applied layer thickness of the coating or more specifically the ash crust that develops from said coating that is applied. Closed profiles, such as pipes, with comparable solidity, need about twice the amount compared to open profiles, such as beams with a double T profile. In order to satisfy the required periods of fire resistance, the coatings have to have a certain thickness and must have the ability to form, when subject to the effect of heat, an ash crust that is as voluminous as possible; and, as a result, this ash crust has good insulating properties and stays mechanically stable over the period of time that it is exposed to a fire.
To this end there are a number of systems in the state of the art. In essence a distinction is made between 100% systems and systems that are based on a solvent or water. In the solvent based or water based systems binders, usually resins, are applied on the component as a solution, dispersion or an emulsion. These solvent based or water based systems can be designed as a single component system or as a multi component system. After the system has been applied, the solvent or water evaporates and leaves behind a film that dries with time. In this case a distinction may also be made between such systems, in which essentially the coating no longer changes during the drying phase, and such systems, in which, following evaporation, the binder is primarily cured by oxidation reactions and polymerization reactions, a process that is induced, for example, by the atmospheric oxygen. The 100% systems contain the constituents of the binder without solvents or water. Said 100% systems are applied on the component in such a way that the “drying” of the coating takes place only by the reaction of the binder constituents with each other.
The solvent based or water based systems have the disadvantage that the drying times, also called the curing times, are long and, in addition, several layers have to be applied, thus necessitating several working steps, to achieve the necessary layer thickness. Since each individual layer has to be suitably dried before the next layer is applied, the result is, on the one hand, a considerable amount of labor in terms of time and correspondingly high costs and a delay in the completion of the building, because depending on climatic conditions it may take several days before the required layer thickness has been applied. Another drawback is that there is the tendency for coatings that exhibit the required layer thickness to form cracks or to flake off during the drying phase or when subject to the effect of heat, so that in the worst case the substrate is partially exposed, in particular, in systems, in which the binder does not reharden after evaporation of the solvent or the water.
In order to circumvent this drawback, two component systems or multi component systems based on epoxy/amine have been developed that more or less make do without any solvents, so that the curing takes place much faster and, in addition, thicker layers can be applied in a single working step, so that it is possible to build up the required layer thickness much faster. However, these two component systems or multi component systems have the drawback that the binder forms a very stable and rigid polymer matrix, often with a high softening range, a phenomenon that hinders the formation of foam by the foaming agent. Therefore, thick layers have to be applied in order to generate a sufficient foam thickness for the insulation. This in turn is disadvantageous because a lot of material is required. In order for these systems to be applied, processing temperatures of up to +70 deg. C. are often required, a feature that makes the use of these systems labor intensive and expensive to install. Furthermore, some of the binder components that are used are toxic or critical in some other way (for example, irritant, caustic), such as, for example, the amines or amine mixtures that are used in the epoxy/amine systems.
In the field of coatings it is known from DE 4141858 A1 to use bisphenol A diglycidyl ethers, which are extended with dimercapto compounds or mercapto-carboxylic acids and bisphenol A, as a binder that is cured with amines. As a result, it is possible to formulate coatings with a high filler content. However, in this case, too, critical compounds are used. WO 2012/082224 A1, for example, describes a composition that comprises at least one epoxy compound, at least one polythiol compound as a curing agent and at least one catalyst. The coatings, which are obtained, among other things, in this way, exhibit a good resistance to solvents and have a hard surface. However, a fire retardant coating on this basis, that contains fire retardant additives, is not known. Furthermore, neither the maximum amount of the fire retardant additives in this fire retardant coating nor the behavior of the coating upon exposure to heat is known.